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Isoprinosine Info Sheet

May 1996

What Is It Really?

Isoprinosine (inosine pranobex) is an old drug that has been extensively studied and used in many countries for herpes, genital warts, influenza, melanomas, other tumors, hepatitis B, and a rare brain inflammation in children caused by the zoster virus (subacute sclerosing panencephalopathy). No one really knew how it worked (not that it always did) until someone noticed that it seemed to be boosting people's immune response, perhaps by helping the body recognize that it was under attack. When the AIDS crisis struck, it was one of the first drugs evaluated.


The Theory Behind Isoprinosine

Isoprinosine does not have any effect on HIV itself. Instead, it has been reported to stimulate various T cell, and other immune cell functions in both test tube and clinical studies. However, the way it does this Ñ its mechanism of action Ñ is not known. Furthermore, the data is often contradictory. Taken as a whole, the data suggest that isoprinosine helps the cell mediated immune response, the part of the immune system responsible for destroying diseased human cells in the body (as opposed to fighting viruses, bacteria or other infectious organisms swimming in your blood). Many studies say that this immune boosting effect is modest, and the immune restoration only partial.


Clinical Studies in PWAs

The first small studies of isoprinosine reported positive results, including rises in CD4 cell counts. Larger subsequent studies did not show CD4 cell rises. One study gave a twenty-eight day regimen of two doses of isoprinosine or placebo to 63 HIV positive patients with ARC or swollen lymph glands, and then monitored these patients for a year. The study concluded that half of the patients who took 3 grams of isoprinosine had significant clinical improvement, and most had sustained increases in natural killer cells, total lymphocytes and CD4/CD8 ratios. Another study in combination with ribavirin reported no immunological benefits whatsoever. In fact, people suffered unexpected drops in their white blood cell counts. Three larger clinical studies examining isoprinosine in HIV-infected people report very conflicting results. Bad News From The Sponsor: The Newport Pharmaceutical study examined 696 HIV-infected, asymptomatic men with T cells between 200 and 400 in the United States and Britain. Half the men received 4 grams of isoprinosine per day; the other half, a placebo. After six months, no difference was seen between the placebo and isoprinosine.


Mediocre News From Italy

Another study, conducted in Italy, followed 553 asymptomatic patients. Patients were given 3 grams of isoprinosine a day, or a placebo for three months. After one year, researchers claimed that there was a slightly improved clinical condition in the people on isoprinosine. Also, their CD4/CD8 ratios were preserved better than patients given placebo. Great News From Denmark: In a Danish study 866 people with a wide range of T cells were given either 3 grams of isoprinosine per day or placebo. After 6 months, the isoprinosine group had far fewer cases of AIDS Ñ indicating that isoprinosine significantly delayed progression to disease. At the same time, however, isoprinosine had no effect on p24 antigen or any immune parameter such as T cell levels.


Making Sense of the Clinical Data

This is one of those cases where there is widely contradictory data on the drug. It is hard to just dismiss any of the above studies - although each had some flaws. A number of explanations have been suggested. One test tube study notes that a metabolite (by-product) of isoprinosine has anti-PCP activity. Participants in the Danish study took no PCP prophylaxis, and most of the patients on placebo that progressed came down with PCP. Isoprinosine may simply have kept treated patients from developing this opportunistic infection, and its benefit had nothing at all to do with immune reconstitution. Another possibility is that isoprinosine could slow progression because of its anti-herpes activity. Dosing regimens also appear to be very important with some immune modulators. Taking an immune modulator for a month, and then stopping treatment could be better than continual use, which may make your system too acclimated to respond to the drug. In many of the smaller isoprinosine studies that reported immunologic changes, people were given drug a short length of time, e.g. one month, and then monitored. One doctor in Switzerland gives his patients two months of isoprinosine followed by a wash-out period. Nevertheless, right now, it is unclear how, or if, the drug helps people with HIV. This is another drug caught in limbo - contradictory data and no on-going studies to resolve the dispute.


Other Studies of Isoprinosine Herpes, Zoster, EBV

In clinical trials, acyclovir consistently out-performs isoprinosine. But, a number of studies report that the combination is superior to either drug alone.


Molluscum

One small study reports positive results treating molluscum in HIV negative children.


Genital Warts

A study in 165 "heterosexual" men and women with genital warts reported that isoprinosine was more effective than conventional treatment (podophyllin or cryotherapy or electrocautery) for older warts, and conventional treatment was superior for more recent lesions. Combination therapy (1 gram isoprinosine 3 times a day for one month plus conventional treatment) increased the success rate from 41% to 94%.


Side Effects and Toxicity

Isoprinosine seems to be well tolerated. The few side effects reported included: dizziness, problems with digestion (for example, slight stomach pain and feeling full after you ate only a small amount of food), and itching. As noted above, when given with ribavirin, there was a drop in people's white blood cell (lymphocyte) counts. People who take AZT and isoprinosine together have been shown to sustain higher levels of AZT in their blood.


Dosing

There is no way to know what the proper dose is. However the clinical studies thus far have examined between 1 - 4 grams per day. The Danish study used 1 gram three times a day. The tablets we distribute are 500 MG each. To take the doses used in the studies, you would take between 2 and 8 tablets every day. To our knowledge, only one study has evaluated how isoprinosine is absorbed and excreted in humans. This study demonstrated that isoprinosine doesn't stay in the body very long. To keep consistent levels of isoprinosine in the body would require fairly frequent oral doses, three or more times a day. Taking isoprinosine as an injection or an enema may deliver initially higher doses into the blood, but the body eliminates this isoprinosine just as quickly. We don't know whether the body requires consistent levels of an immune modulator in order to respond to it, but if it does, oral dosing is the easiest way to acheive this.


What We Carry

We carry isoprinosine made by Newport Pharmaceuticals. It comes in boxes of 20 tablets of 500 MG each.




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